set1 = set("c.biancheng.net")
set2 = set([1,2,3,4,5])
set3 = set((1,2,3,4,5))
print("set1:",set1)
print("set2:",set2)
print("set3:",set3)

set1 = {1,2,3}
set2 = {3,4,5}

# set1 有，而 set2 没有的元素，放到set3 中，并返回
set3 = set1.difference(set2)
print(set3)

v = set1.pop()
print(v)
print(set1) # 第一个元素被删除了

v = set2.remove(5)
print(v)
print(set2)

